Yesterday (22 March 2020) we launched the inaugural World Pigment Day. There was an huge amount of engagement on social media and particularly on Instagram. Over the next few days I will be sharing images and pigment stories from people who posted to celebrate World Pigment Day. First up is artist Polly Bennett, a resident of St Ives in Cornwall, who contributed a series of posts on the colours of the Rainbow. Over to Polly …

Red: Cinnabar Cinnabar is a toxic mercury sulfide mineral that has been used as a pigment for thousands of years due to its bright red colour. It is a pigment in its own right, however, it was also used to make the red pigments known as “vermilion” and “Chinese red”. Cinnabar is a hydrothermal mineral that is usually found in rocks surrounding recent volcanic activity but can also form near hot springs and fumaroles (an opening in or near a volcano). Because of cinnabar’s toxicity, it is a lot less commonly used nowadays.

Orange: Ochre Ochre is a family of earth pigments that includes yellow ochre, red ochre, purple ochre, sienna, and umber. It consists of varying amounts of iron oxide, clay and sand, and ranges in colour from yellow to deep orange or brown with an array of shades inbetween. I have found huge amounts of ochre earth in St Ives, where I am currently staying, and have been slowly but surely grinding and separating the ochre into different shades. The mineral goethite, an iron oxide hydroxide and the main constituent of most yellow ochres, is named after Johann Wolfgang von Goethe, the colour scientist whose death marks the date of World Pigment Day

Yellow: Sulphur Although Sulphur is not a pigment, I found some in a curio shop and was curious to see if it ground into a powder; would it work in the same way?  So I intend to turn it into watercolour and test it out. Historically it has been used to bleach cloth, so it might do something similar when applied over the top of other watercolours. Sulphur occurs naturally as the element, often in volcanic areas, and as the extraction of pigments is very alchemical, I thought it was interesting to note that for centuries, along with mercury and salt, it was believed to be a component of all metals and formed the basis of alchemy, whereby one metal could be transmuted into another.

Green: Green Earth from St Ives Yesterday I was super excited to find a little green sparkly rock on the eroded foreshore. I set about grinding it down and managed to get two shades of green from it, the darker one I immediately made into watercolour.

 

 

Blue: Azurite Azurite is a soft copper mineral, named for its beautiful “azure blue” colour. It has been ground and used as a pigment in blue paint as early as ancient Egypt, and through time, its become much more common. During the Middle Ages and Renaissance, it was the most important blue pigment used in Europe, and through the early 19th century, it was also known as chessylite, after the type locality at Chessy-les-Mines near Lyon, France, where much of the pigment was mined. Here I have mullered the Azurite into glaze.

Indigo: Mussel Shell Blue from St Ives Since landing in St Ives I have been going down to the foreshore every morning to collect mussel shells as I wanted to create a blue pigment to represent the sea, however after being ground the mussels create a light indigo colour that I love! Historically painters used shells as paint pans, so I thought it very appropriate to make watercolour paint with the mussel pigment and use one of the mussel shells as the pan for the paint.

Violet: Cochineal Cochineal is a bright scarlet insect lake pigment that has been used for centuries to dye textiles, drugs, food and cosmetics. A lake pigment is a pigment made by precipitating a dye with a mordant. Unlike mineral pigments, lake pigments are organic.Cochineal is the result of harvesting the female cochineal parasitic insect that live on the cacti native to Mexico, Central and South America. Using soda ash and alum, I extracted the pigment from the insects and added honey and gum arabic to make watercolour.

Follow Polly on Instagram.

 

Professor David Dobson was UCL Slade School Scientist in Residence for 2017-2018. Intrigued my the media coverage that the development of the new YIn Mn Blue pigment made in 2017, David was moved to make his own blue and think more about blue minerals in the Earth. David has recently been interviewed in Science Magazine by Kai Kupferschmidt.

David writes …

We live on the blue planet. Blue is so common in our everyday experience that we don’t even notice it. The sky is blue due to light scattering and water absorbs short wavelengths of the visible spectrum making it a pale blue.  But blue minerals are rare; so much so that in medieval and renaissance time blue pigments were reserved for God and the saints.  Most mineral colouration comes from small amounts of transition metal impurities in the mineral structure.  This class of element can exist in several different electrical charge states and the hopping of electrons from one transition metal ion to another causes absorption of light in the visible spectrum and hence colour.

Iron, with allowed charges of 2+ or 3+, is the most common transition metal and so most minerals display the colours associated with electron hopping between 2+ and 3+ iron – red or brown when 3+ dominates and green when 2+ dominates. But deep in the Earth’s interior, at pressures of 180 to 230 thousand atmospheres the most common mineral, ringwoodite, is a rich royal blue. Once again, water is responsible, at least in part. In this case water is incorporated into ringwoodite as protons (H⁺ ions) and it substitutes for the main cations, Mg²⁺ or Si⁴⁺. In order for a stable substitution in a crystal lattice the charges must balance – you can’t replace one silicon (Si⁴⁺) ion for just one proton because the crystal would be left with an excess negative charge which would blow it apart.  Instead the proton is accompanied by an iron ion to make a [Fe³⁺H⁺] substitution on the silicon site.  This pushes the iron into a much smaller site than it usually occupies, surrounded by only 4 oxygen (O^2-) ions rather than the usual 6 oxygens.  This in turn changes the energy of charge transfer electron hopping transitions between iron 2+ and 3+ ions, making ringwoodite blue rather than brown. This [Fe³⁺H⁺] substitution is such a good fit in the silicon site that, if all the ringwoodite in the Earth had as much water as possible in its structure (and that is a BIG if), there could be as much as 4 time the entire volume of the oceans locked up as structurally bound water in the Earth’s mantle and Earth’s interior would be as blue as its exterior.

Here in UCL Earth Sciences we are attempting to develop synthetic structures which mimic the unusual ferric iron structure of ringwoodite but which are stable at atmospheric pressure.  So far we have shown that we can make blue pigments from iron-bearing oxides and are now investigating how much Fe³⁺ the structures can take before they become unstable.  That will determine just how blue we can make them. The prospects are bright…blue.

Ringwoodite synthesised at 20 GPa and containing 10% iron

 

David’s new blue, with about 0.3% iron

 

Three blues created by Fe2+-Fe3+ charge transfer: vivianite (in the centrifuge vial), (on the left) my Fe-bearing zinc germanate with Fe from 0 to 0.3% and (on the right) a Fe-dopes zinc silicate.

 

A a cross- and interdisciplinary event at the UCL Slade School of Fine Art to celebrate International Colour Day and World Poetry Day took place on 20th and 21st March 2019. This included all things colourful and poetic and often both, from talks, poetry readings, to making and mixing pigments, and looking at images in the accompanying exhibition The Nomenclature of Colours.

The symposium was conceived and organised by Jo Volley of the Slade School and the exhibition The Nomenclature of Colours was curated by Jo and Stephanie Nebbia. The photos used here were taken by Gabriela Giroletti and Ruth Siddall.

The full programme is available here.

 

Speakers talking about colour and research were; Michael Berkowitz, Malina Busch, Jane Bustin, Mark Cann, David Dobson, Taylor Enoch, Roland-Francois Lack, Liz Lawes, Andy Leak, Antoni Malinowski, Onya McCausland, Dimitris Mylonas, Ruth Siddall, Henrietta Simson, Estelle Thompson and Edward Winters.

The poets who read from their work were Mataio Austin Dean, Rhun Jones, Sharon Morris, Fabian Peake and George Szirtes. Caroline de Lannoy‘s ‘Colour Tale’ was performed by Caroline and Slade School students, the ‘Colour Tale Choristers’.

David Dobson, Ian Rowlands and Jo Volley demonstrated making and mixing pigments.

Looking at Josef Albers’s silk screen prints from the Slade’s edition of Interaction of Colour in a talk and discussion led by Malina Busch.

An exhibition of pigments in the Material Museum curated by Jo Volley.